In prior art reaction systems the reaction temperature inside the reactor is controlled by regulating the amount of added initiator, or by providing indirect cooling by means of cooling pipes.
GB Patent No. 1,538,633 teaches a high pressure process for polymerizing monomer comprising ethylene in a first and second autoclave reaction zones arranged in series, which process is performed with a reduced temperature in said first zone in order to obtain final products having improved optical properties. The average amount of monomers fed to the first part of the reactor is reduced, thus obtaining an improved distribution of the polymerization reactions along the reactor. The temperature is controlled by regulating the introduced amount of initiator.
U.S. Pat. No. 3,299,033 discloses a method used in a high pressure ethylene polymerization process to provide a substantially uniform feeding rate of initiator into the reactor by means of a temperature or pressure controlled valve arranged in the feeding line. The main purpose of the invention is to smooth out the variations in the amounts of initiator delivered by the piston pumps used for feeding the initiator, as well as smoothing out the variations caused by pressure fluctuations in the reactor. The initiator is mixed with ethylene to achieve improved mixing.
U.S. Pat. No. 4,012,573 teaches a method of removing heat from polymerization reactions of monomers in the gas phase in a reactor by removing a portion of the gaseous monomers, liquefying said monomers and regulate the rate at which the liquid is fed back to the reactor, whereby the temperature and pressure inside the reactor are regulated.
DE Patent No. 2,611,405 teaches the introduction of cooling pipes into the reactor to remove reaction heat.
DE Patent No. 1,620,947 teaches the conveying of cold ethylene through a heat exchange unit mounted inside the reactor. The cooling effect of the cold ethylene is used for indirect cooling of the reactor, and the prewarmed ethylene is fed to the reactor.
These patents do not suggest the use of any control system for regulating the amounts of initiator and monomer, alternatively cold monomer, fed directly into the reactor with the purpose of controlling the temperature inside the reactor.
Attempts which are made in the prior art to regulate the reacion temperatures within an autoclave reactor of relevant type by varying the amounts of introduced initiator often result in large temperature variations. In contrast thereto the present process for the production of olefin polymers in an autoclave reactor makes it possible to keep the reaction temperature within a predetermined range, i.e. with only minor deviations from a preset temperature. As a consequence thereof, the polymerization reaction rate can be controlled throughout the reactor length.